The present invention relates to a valve device for controlling pressure actuated brakes for railway and other vehicles wherein a multi-stage valve is used to set one of a plurality of pressure stages, more particularly to the maintaining of the pressure applied to the brake at each braking stage within precise predetermined standards.
It is known to control pressure medium actuated brakes, particularly in railway vehicles, by using a multi-stage valve in which is slidably mounted an axially displaceable stepped piston having a plurality of annular radial surfaces with a predetermined surface ratio to each other. These surfaces can be subjected to the action of pressure medium through control valves separately or in combination in accordance with a predetermined pressure stage. The piston controls a double valve connected between a source of pressure medium and the brake which is supplied with pressure medium or vented in response to the position of the double valve.
German patent 718 414 discloses a device for controlling the brakes of railway vehicles wherein distribution elements for regulating the operating medium are arranged on the different cars. A multi-stage brake regulating switch is employed which has a number of brake positions corrresponding to the number of braking stages and which is provided with a number of driving elements correspondng to such braking positions. The elements are electrically controlled. In response to the electrical setting of such driving means, the distribution element is shifted into the setting which corresponds to the specific setting of the brake regulating valve.
British patent 903 600 discloses an automatic multi-stage valve which when open will permit the brake cylinder to become filled with a pressure medium until the valve is closed in response to a reaction from the filled brake cylinder. The valve is thus closed and the brake is maintained in the release position by means of a unilaterally open tube which forms the axis of the displaceable control valve. The position of the brake can be varied by stages that are established by the control valve. Such known devices generally employ multi-stage or graduated valves that have a constant pressure stage level. This means that the same brake force is effective at every pressure or braking stage. As a result, the percentage deviation in the separate pressure stages is different which may lead to an undesirable shaking and shifting in the separate cars. If it is desired to apply the braking force in response to the load of the vehicles, then special structure such as valves and accessories thereto must be connected to the multi-step valve. The result is a complex and expensive braking system.